CN113353061A - Four-motor-driven FSAE racing car electronic differential algorithm based on sliding mode control - Google Patents

Abstract

The invention discloses a sliding mode control-based electronic differential algorithm for a four-motor-driven FSAE racing car, which comprises the following steps of: constructing a two-degree-of-freedom vehicle model, and calculating an ideal yaw rate according to the two-degree-of-freedom vehicle model and vehicle sensor data; constructing a sliding mode variable controller, and calculating the required yaw moment through the sliding mode variable controller; the invention provides a torque control electronic differential algorithm of a four-motor-driven FSAE racing car based on slip film control, which not only controls torque output of inner and outer wheels during steering to improve the steering stability of the car, but also controls the yaw moment of the car to approach to a stable direction by allocating the torque of each wheel, thereby improving the limit of the racing car.

Description

An Electronic Differential Algorithm for Four-motor Driven FSAE Racing Car Based on Sliding Mode Control

technical field

The invention relates to the technical field of four-motor-driven FSAE racing car control, in particular to a four-motor-driven FSAE racing car electronic differential algorithm based on sliding mode control.

Background technique

The China Formula Student Competition is an automobile design and manufacturing competition organized by students from related majors in colleges and universities. Each participating team designed and manufactured a small single-seater recreational racing car within one year in accordance with the competition rules and racing car manufacturing standards, which was able to successfully complete the competition. The race is divided into oil car group, tram group and unmanned car group. Among them, trams have three driving schemes: single-motor, dual-motor and four-motor drive.

In recent years, due to the excellent performance of the four-motor drive in terms of power and maneuverability, the number of fleets using the four-motor drive has increased year by year.

Four-motor drive uses four motors to directly drive the four wheels, eliminating the traditional mechanical differential. When turning or driving on uneven roads, the outer wheel needs to rotate faster than the inner wheel. If the inner and outer wheels are still used at this time. If the torque output is the same, not only the grip performance of the tires cannot be fully exerted, but it may also cause the vehicle to be excessively understeered, and the gear box parts are under severe stress, which will adversely affect the vehicle handling stability.

To solve this problem, the electronic differential system is the main solution in the car. On this issue, many control strategies have been applied. For example, based on the Ackerman steering model, the target values of inner and outer wheel speeds are obtained, and then PI control or sliding mode control is used to control the speed of the driving wheels.

Although the above work has made great progress in improving vehicle performance, it has not fully exploited the advantages of four-motor-driven racing cars that can directly and independently control the driving torque of each wheel, and has not fully considered whether the tire performance is fully utilized. Therefore, in order to better improve the vehicle handling stability, torque control can be considered for electronic differential. Therefore, the present invention proposes an electronic differential algorithm of four-motor drive FSAE racing car based on sliding mode control to solve the above-mentioned problems in the background art.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a four-motor-driven FSAE racing electronic differential algorithm based on sliding mode control, so as to solve the problems raised in the above background technology.

To achieve the above object, the present invention provides the following technical solutions:

A four-motor drive FSAE racing electronic differential algorithm based on sliding mode control includes the following steps:

Build a two-degree-of-freedom vehicle model, and calculate the ideal yaw rate based on the two-degree-of-freedom vehicle model and vehicle sensor data;

Build a sliding mode controller, and calculate the required yaw moment through the sliding mode controller;

The torque distribution algorithm is constructed, the torque distributed by each required wheel is calculated, and the torque distribution is performed.

As a further solution of the present invention: according to Newton's second law, the two-degree-of-freedom vehicle model is specifically:

Among them, a, b are the distance from the center of mass to the front and rear axles, C _F , C _R are the cornering stiffness of the front and rear axles, m, I _Z are the body mass and the moment of inertia around the Z axis, β, γ, δ, u are the center of mass side deflection, respectively angle, yaw rate, front wheel angle, longitudinal speed, lateral speed;

When the car is stable, all derivative terms are zero, and we get:

in,

As a further scheme of the present invention: the sliding mode surface is selected as the difference between the actual yaw rate γ and the target yaw rate γ _d , the difference between the actual side slip angle β _d and the target side slip angle β _d , where c is a constant ,

s=(γ-γ _d )+c(β-β _d )

After entering the sliding surface:

which is:

As a further scheme of the present invention: the yaw motion equation of the racing car is:

Simplified to:

Among them, since the yaw moment required by the whole vehicle can be provided by four wheels, namely:

Bring M _z into, then:

时，得理想的横摆力矩M_eq为：As a further solution of the present invention: when s'=0, that is,

When , the ideal yaw moment M _eq is:

As a further solution of the present invention: in the sliding mode variable structure control, the input of the control system is written as M _z =M _eq +M _vs , where M _eq is the control quantity of the sliding mode surface obtained by the system when there is no external factor influence, M _vss is the control quantity of the system under the action of various external disturbances; in order to make the system approach the sliding mode surface quickly and stably, the control system approaches the sliding mode surface according to the exponential law, which approaches the control law. which is:

s'=-ξsgn(s)-ks, where ξ>0, k>0.

As a further scheme of the present invention: the switching control function is:

M _vss =M _z -M _eq =I _z (-ξsgn(s)-ks)

Then the yaw moment output is:

As a further scheme of the present invention: according to:

Calculate the left and right wheel moment deviation required to obtain the target yaw rate, where t _f , _tr , a are the distance between the front and rear wheelbase and the center of mass to the front axle, respectively, and R is the wheel radius.

As a further scheme of the present invention: the torque distribution formula is:

Compared with the prior art, the beneficial effects of the present invention are:

1. The present invention proposes a four-motor drive FSAE racing car torque control electronic differential algorithm based on sliding film control, which not only controls the torque output of the inner and outer wheels during steering to improve the steering stability of the vehicle, but also adjusts the rotation of each wheel. The yaw moment of the vehicle is controlled to approach the stable direction, which improves the limit of the racing car.

2. The sliding mode control of the present invention has the advantages of fast response, insensitive to parameter changes and disturbances, no need for online identification of the system, simple physical implementation, etc. The controller constructed for a highly nonlinear object such as a vehicle can effectively reduce sensor interference Influence, control has good application value.

3. The electronic differential algorithm realized by the present invention can effectively improve the stability and steering limit performance of the four-motor-driven FSAE racing car under steering conditions.

Description of drawings

Figure 1 is a flow chart of a four-motor drive FSAE racing electronic differential algorithm based on sliding mode control.

Figure 2 is a graph of the yaw rate in a four-motor-driven FSAE racing electronic differential algorithm based on sliding mode control.

Figure 3 is a graph of the center of mass slip angle in a four-motor drive FSAE racing electronic differential algorithm based on sliding mode control.

Figure 4 is a graph of lateral acceleration in a four-motor drive FSAE racing electronic differential algorithm based on sliding mode control.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Referring to FIGS. 1 to 4 , in an embodiment of the present invention, a four-motor-driven FSAE racing electronic differential algorithm based on sliding mode control includes the following steps: constructing a two-degree-of-freedom vehicle model, according to the two-degree-of-freedom vehicle model and vehicle sensors. Data, calculate the ideal yaw angular velocity; build a sliding mode controller, through the sliding mode controller, calculate the required yaw moment; build a torque distribution algorithm, calculate the torque distributed by each required wheel, and perform torque distribution .

According to Newton's second law, the two-degree-of-freedom vehicle model is specifically:

Among them, a, b are the distance from the center of mass to the front and rear axles, C _F , C _R are the cornering stiffness of the front and rear axles, m, I _Z are the body mass and the moment of inertia around the Z axis, β, γ, δ, u are the center of mass side deflection, respectively angle, yaw rate, front wheel angle, longitudinal speed, lateral speed;

When the car is stable, all derivative terms are zero, and we get:

in,

The sliding surface is selected as the difference between the actual yaw rate γ and the target yaw rate γ _d , the difference between the actual side slip angle β _d and the target side slip angle β _d , where c is a constant,

s=(γ-γ _d )+c(β-β _d )

After entering the sliding surface:

which is:

The yaw motion equation of the car is:

Simplified to:

Among them, since the yaw moment required by the whole vehicle can be provided by four wheels, namely:

Bring M _z into, then:

时，得理想的横摆力矩M_eq为：When s'=0, that is

When , the ideal yaw moment M _eq is:

In the sliding mode variable structure control, the input of the control system is written as M _z = M _eq + M _vss , where M _eq is the control quantity of the sliding mode surface when the system is not affected by any external factors, and M _vss is the system when there are various The control quantity of the system under the action of external disturbance; in order to make the system approach the sliding mode surface quickly and stably, the control system approaches the sliding mode surface according to the exponential law approaching the control law, namely:

s'=-ξsgn(s)-ks, where ξ>0, k>0.

The switching control function is:

M _vss =M _z -M _eq =I _z (-ξsgn(s)-ks)

Then the yaw moment output is:

according to:

Calculate the left and right wheel moment deviation required to obtain the target yaw rate, where t _f , _tr , a are the distance between the front and rear wheelbase and the center of mass to the front axle, respectively, and R is the wheel radius.

The torque distribution formula is:

Finally, the joint simulation of carsim/simulink shows that the electronic differential method of torque control proposed by the present invention can improve the lateral limit of the racing car, reduce the side slip angle and yaw angular velocity of the center of mass during steering, and improve the lateral stability. The lateral control of motor-driven racing cars has practical value.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or change of the inventive concept thereof shall be included within the protection scope of the present invention.

Claims (9)

1. a four-motor drive FSAE racing electronic differential algorithm based on sliding mode control, is characterized in that, comprises the following steps: Build a two-degree-of-freedom vehicle model, and calculate the ideal yaw rate based on the two-degree-of-freedom vehicle model and vehicle sensor data; Build a sliding mode controller, and calculate the required yaw moment through the sliding mode controller; The torque distribution algorithm is constructed, the torque distributed by each required wheel is calculated, and the torque distribution is performed. 2. a kind of four-motor-driven FSAE racing electronic differential algorithm based on sliding mode control according to claim 1, is characterized in that, according to Newton's second law, described two degrees of freedom vehicle model is specifically:

Among them, a, b are the distance from the center of mass to the front and rear axles, C _F , C _R are the cornering stiffness of the front and rear axles, m, I _Z are the body mass and the moment of inertia around the Z axis, β, γ, δ, u are the center of mass side deflection, respectively angle, yaw rate, front wheel angle, longitudinal speed, lateral speed; When the car is stable, all derivative terms are zero, and we get:

in,

3. a kind of four-motor drive FSAE racing electronic differential algorithm based on sliding mode control according to claim 1, is characterized in that, choosing sliding mode surface is the difference value of actual yaw rate γ and target yaw rate γ _d , the difference between the actual slip angle β _d and the target slip angle β _d , where c is a constant, s=(γ-γ _d )+c(β-β _d ) After entering the sliding surface:

which is:

4. a kind of four-motor drive FSAE racing electronic differential algorithm based on sliding mode control according to claim 1 is characterized in that, the yaw motion equation of racing is:

Simplified to:

Among them, since the yaw moment required by the whole vehicle can be provided by four wheels, namely:

Bring M _z into, then:

5. A four-motor driving FSAE racing electronic differential algorithm based on sliding mode control according to claim 4, characterized in that, when s'=0, that is,

When , the ideal yaw moment M _eq is:

6. a kind of four-motor drive FSAE racing electronic differential algorithm based on sliding mode control according to claim 5, is characterized in that, in sliding mode variable structure control, the input of control system is written as M _z =M _eq +M _vss , where M _eq is the control quantity of the sliding mode surface when the system is not affected by any external factors, and M _vss is the control quantity of the system under the action of various external disturbances; The control system approaches the sliding mode surface with the exponential approach approaching the control law, namely: s'=-ξsgn(s)-ks, where ξ>0, k>0. 7. a kind of four-motor drive FSAE racing electronic differential algorithm based on sliding mode control according to claim 6, is characterized in that, switching control function is: M _vss =M _z -M _eq =I _z (ξsgn(s)-ks) Then the yaw moment output is:

8. a kind of four-motor drive FSAE racing electronic differential algorithm based on sliding mode control according to claim 7, is characterized in that, according to:

Calculate the left and right wheel moment deviation required to obtain the target yaw rate, where t _f , _tr , a are the distance between the front and rear wheelbase and the center of mass to the front axle, respectively, and R is the wheel radius. 9. a kind of four-motor drive FSAE racing electronic differential algorithm based on sliding mode control according to claim 7, is characterized in that, torque distribution formula is:

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